Injection molding machines are used to produce molded parts of almost any shape. The respective tool only needs to include cavities into which molten plastic can be injected. In the working position for example, the parts of the tool that are separated by a separation plane are firmly pressed together hydraulically. After the plastic has been injected into the cavities of the tool, it usually remains closed in the conventional technique, until the molded parts in the cavities have sufficiently cooled and solidified so that they can be removed from the tool. To that end the tool is opened along the separation plane and its parts are separated from each other. During the time when the plastic of the molded parts cools, the injection molding machine is not used. This disadvantage is particularly significant when relatively thick-walled molded parts which require an extended cooling period are being produced.
The output of an injection molding machine can be increased if a tool is used that works in tandem according to the cited German magazine “Plastics 84”. In an injection molding machine that operates with such a tool, the parts alternately open along two separation planes. During the cooling time of the molded parts in one separation plane, the molded parts can be removed from the other separation plane. This operation is advantageous for molded parts with a cooling period that is longer than the metering time needed to fill the cavities. Injection molding machines which operate in tandem are very special expensive machines. They require a moveable central plate that is installed in the middle, and to which the injection molding unit is laterally attached. The molten plastic is injected into the respective cavities through channels located in the central plate. This known tandem technique cannot be installed in conventional injection molding machines, or only after extensive rebuilding.